1. Usability engineering

2. Software Quality (ISO 9126)
Metrics and Evaluation
Functionality
Reliability
Usability
Efficiency
Maintainability
Portability
PM Accessibility (sometimes relevant, not ISO 9126)

3. Definition of Usability (Nielsen 2003)
Usability: how well users can use the system’s functionality
Usability is a quality attribute that assesses how easy user interfaces are to use
The word ‘usability’ also refers to methods for improving ease-of-use during the design process

4. Usability Components Learnability Throughput (also Efficiency)
Ease of learning the system, i.e. the basic tasks
Skills retained over time (also Memorability)
Throughput (also Efficiency)
Speed of task performance
Low user error rate
Flexibility
Suitability for intended user expertise
Can system be customised?
Attitude (also Satisfaction)
User subjective satisfaction with system

5. Usability Components (Dimensions of usability)
Learnability: is it easy to learn?
Memorability: is it easy to remember what you learned?
Efficiency: once learned, is it fast to use?
Errors: are errors few and recoverable?
Satisfaction: is it enjoyable to use?

6. The 5E’s to Usability Easy to learn
Supports initial learning and continued learning
Efficient
The speed in which users complete their tasks
Error tolerant
The ability of the interface to prevent errors or help users recover from those that occur
Effective
The completeness and accuracy with which users achieve their goals
Engaging
How pleasant or satisfying the interface is to use?

7. Usability Engineering
The test of usability based on measurement of user experience
It demands that specific usability measures be made explicit as requirements
Usability Measurements
Usability attribute/principle
Measuring concept
Measuring method
Now level/ worst case/ planned level/ best case

8. Some metrics from ISO 9241
Usability Effectiveness Efficiency Satisfaction objective measures measures measures
Suitability Percentage of Time to Rating scale for the task goals achieved complete a task for satisfaction
Appropriate for Number of power Relative efficiency Rating scale for trained users features used compared with satisfaction with an expert user power features
Learnability % of functions Time to learn Rating scale for learned criterion ease of learning
Error tolerance % of errors Time spent on Rating scale for corrected successfully correcting errors error handling

9. Usability Engineering (contd.)
Problems
usability specification requires level of detail that may not be
possible early in design satisfying a usability specification
does not necessarily satisfy usability

10. Case Study-ATM (from L9)
Researchers + banks expected ATMs to be intuitively easy to use
Testing among senior citizens found only 20% correct operation
Senior citizens often put off by ATMs they find the machines
Complicated
Inconvenient

11. Problems with ATMs Buttons that did not line up with commands
Screens hard to read in the glare of daylight
Sometimes confusing menu choices

12. Usability suggestions
Simpler on-screen instructions
More “undo” buttons
Bank should provide training for any customers who need it
Remark:
“Large percentage” of people surveyed said they would use ATMs if trained

13. Key concepts of HCI Usability Cognetics- locus of attention Affordance
What sort of operations and manipulations can be done to an object
Crucial is the perceived affordance
Visibility
Mapping between controls and effects should be sensible and meaningful
feedback
Task orientation- fit, analysis

14. Important principle of HCI (Usability)
useful
Accomplish what is required (functional, does things)
usable
Do it easily and naturally without error (does the right things)
used
Make people want to use it (be attractive, acceptable to organization)